As Earth orbits the Sun, it plows through the dust and debris left behind by comets and asteroids. That debris gives rise to meteorites – what may be one of nature’s most amazing spectacles.
Most meteor showers are predictable, recurring annually when Earth crosses a characteristic trail of debris.
Occasionally, however, Earth passes through a particularly narrow, dense clump of debris. This results in a meteor storm, causing thousands of shooting stars to move across the sky every hour.
A small shower called the Tau Herculids could produce a meteor storm for observers in the US next week. But while some websites promise “the most powerful meteor storm in generations,” astronomers are a little more cautious.
Introducing Comet SW3
The story begins with a comet named 73P/Schwassmann–Wachmann 3 (Comet SW3 for short). First observed in 1930, it is attributed to a weak meteor shower called the Tau Herculids, which appears to radiate from a point about ten degrees from the bright star Arcturus today.
In 1995, Comet SW3 brightened up suddenly and unexpectedly. Several eruptions were seen in a few months. The comet was catastrophically fragmented, releasing huge amounts of dust, gas, and debris.
By 2006 (two orbits later), Comet SW3 had further disintegrated into several bright fragments with many smaller fragments.
Fragments of Comet 73P as seen by the Hubble Space Telescope in 2006. (NASA, ESA, H. Weaver (APL/JHU), M. Mutchler and Z. Leway (STScI))
Is Earth on a collision course?
This year, Earth will cross the orbit of Comet SW3 in late May.
Detailed computer modeling shows that the debris is spreading in the orbit of the comet like a giant thin tentacle in space.
Has the debris spread far enough to meet Earth? It depends on how much debris was removed in 1995 and how fast that debris was blown outward as the comet broke apart. But the bits of dust and debris are so tiny that we can’t see them until we run into them. So how can we get an insight into what might happen next week?
Can history repeat itself?
Our current understanding of meteor showers began 150 years ago with an event similar to the story of SW3.
A comet named Comet 3D/Biela was discovered in 1772. It was a short-period comet like SW3, returning every 6.6 years.
In 1846 the comet began to behave strangely. Observers observed that its head had split in two, and some described the “architecture of cometary matter” between the fragments.
On the comet’s next return, in 1852, the two fragments were clearly separated and both fluctuated unexpectedly in brightness.
The comet was never seen again.
But in late November of 1872, an unexpected meteor storm took over the northern skies, surprising observers with a rate of more than 3,000 meteors per hour.
The meteor storm occurred when Earth passed 3D/Biela’s orbit: this was where the comet should have been two months earlier. A second storm, weaker than the first, occurred in 1885, when Earth once again encountered the remnants of the comet.
3D/Biela was shattered into rubble, but the two great meteor storms it generated served as a fitting wake-up call.
A dying comet, falling before our eyes, and an associated meteor shower, are usually barely imperceptible against background noise. Are we about to see history repeat with Comet SW3?
What does this tau suggest for Hercules?
The main difference between the events of 1872 and this year’s Tau Hercules comes in the timing of the comet’s crossing of Earth’s orbits. In 1872, Earth passed Beela’s orbit for several months. Afterwards The cause of the comet was, moving through the material where the comet would have been.
In contrast, the next week’s encounter between Earth and the SW3 debris stream lasts several months. before this The comet is due to reach the crossing point. so the debris will have to be dispersed ahead For a comet to be a meteor storm.
Could the debris have spread far enough to meet Earth? Some models suggest that we will see a strong performance from the shower, others suggest that the debris will fall a little.
Don’t count your meteors before they shine!
If anything, observations of next week’s shower will greatly improve our understanding of how comet fragmentation events occur.
Calculations show that Earth will cross SW3’s orbit at around 3 p.m., May 31 (AEST). If the debris reaches far enough to face Earth, the Tau Herculids are likely to explode, but this will only last for an hour or two.
From Australia, the show (if any) will end before it gets dark to see what’s going on.
However, observers in North and South America will have a ringside seat.
They are more likely to see a moderate display of slow-moving meteors than a giant storm. This would be a great result, but could be a bit disappointing.
However, there’s a chance that the shower could actually do a great job. Astronomers are traveling around the world, just in case.
What about Australian observers?
There is also a very small chance that an activity will last longer than expected, or will even come a little later. Even if you’re in Australia, it’s worth visiting on the evening of May 31, just in case you can catch a glimpse of a fragment of a dying comet!
The 1995 debris stream is one of many determined by comets over the past decades.
Tau Hercules is low in the northern sky over Australia – at 7 p.m. local time. (Museum Victoria / Planetarium)
Around 4 a.m. (AEST) on May 31, Earth will pass debris from the comet’s 1892 passage around the Sun. Later that evening, at around 8 p.m., May 31 (AEST), Earth will pass the debris laid by the comet in 1897.
However, the debris from those trips would have spread over time, and so we expect only a few meteors to grace our skies from those streams. But, as always, we could be wrong – the only way to know is to go outside and see! 
Jonty Horner, Professor (Astronomy), University of Southern Queensland and Tanya Hill, Honorary Fellow and Senior Curator (Astronomy) of the University of Melbourne, Museum Victoria.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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